Late last Thursday night, shortly after her rumored split with One Direction’s Harry Styles, Kendall Jenner posted a pic on Instagram that featured the phrase: “don’t let boys be mean to u.” The post was enough to send the band’s fans into a Twitter tizzy over the alleged diss.

It’s the latest example of rabid fans lashing out on social media to defend a beloved celebrity. From Justin Bieber’s “Beliebers” furiously protesting his arrest to Ke$ha’s “Animals” bashing a music producer for her eating disorder, these new fandoms are born of feverous devotion and earnest solidarity.

“It’s not five girls at a sleepover mooning over Harry Styles,” explains Christianna Giordano, a digital strategist at Cohn & Wolfe and blogger for Social Media Today. “It’s 5 million girls chatting on Twitter all day with other crazy fans — that fuels the fire.”

She says celebs with the most devoted online followings succeed by sharing intimate moments with their fans and personally responding to them — thus nurturing a “friendship” that feels quite real: “It’s that intimacy you would have never gotten before social media,” Giordano says.

That passionate intensity isn’t too far a cry from the days of Beatlemania, notes Peggy Drexler, an assistant professor of psychology at Weill Cornell Medical College and author of “Our Fathers, Ourselves: Daughters, Fathers, and the Changing American Family.” What has changed, she says, is the unprecedented interaction with A-listers.

“Social media allows celebrities to give their fans ‘access,’ or, at the very least, the illusion of access,” she says.

That encourages fans to rip into those they believe have wronged their celeb buddy. “The fans can get crazy because they feel they’re defending their friend,” explains Giordano.

Ke$ha

Demographic: Bad girls who follow Ke$ha’s advice to “brush their teeth with a bottle of Jack”

Known for: Despising Dr. Luke, Ke$ha’s producer, whom they blame for stifling the star creatively and the commercial failure of her last album, “Warrior”

Recent dust-up: After Ke$ha announced she was in rehab for an eating disorder earlier this year, the Animals clawed into Dr. Luke, whom a source said told her she “looked like a f - - king refrigerator.” Things got so intense, the LAPD looked into the death threats he was receiving.

Sample tweet: @Bre$ha: “@TheDoctorLuke YOU should go to HELL for making kesha go to rehab because you called her a REFRIGERATOR”

Britney Spears

Known for: Defending the star’s fading vocal and dancing abilities as improving despite all evidence to the contrary; referring to Spears as a deity

Recent dust-up: The Army dispatched its forces against any and all criticism of Brit’s new Vegas residency, which features minimal singing and dancing — although the pop tart does sport a fake painted-on six-pack.

Sample tweet: @jcsef: “@ruff_ ryder_ kill yourself but before you do that buy @ britneyspears’ new single ‘WORK BITCH’ on iTunes now!”

Recent dust-up: His recent stint in rehab got him lots of support, but the biggest upset for fans came in November 2012, when Brown got in a Twitter fight with comedy writer Jenny Johnson. After making sexist remarks, he temporarily deleted his account. Team Breezy picked up the battle with a slew of death threats.

Chris Brown: @DakotaCrimley: “If You A Hater Of Chris Brown Then Go F*** Yourself and Get A Life”

Recent dust-up: When Adam Levine started sub-tweeting Mother Monster with statements like “Ugh . . . recycling old art for a younger generation doesn’t make you an artist. It makes you an art teacher,” he likely soon regretted it, thanks to an uproar from Gaga’s fans.

Rihanna

Photo: W8 Media / Splash NewsTwitter following: 34.3 million

Fan base name: Rihanna Navy

Demographic: Angry girls who like weed and gun tattoos

Known for: Hating #TeamBreezy

Recent dust-up: Last month, a Twitter user (@benvoy) Photoshopped a tweet, making it appear that Rihanna had posted the homophobic: “Arnt u gay? . . . Nuff said blah!” When his fraud was found out, @benvoy paid the price via the Navy’s battleships.

Justin Bieber

Recent dust-up: Last spring, one 15-year-old’s harmless tweet — “Not really a fan of Justin Bieber but his acoustic album is actually good!” — became a nightmare when Bieber himself retweeted it. Beliebers immediately attacked the young girl with death threats.

Known for: Attacking any female linked to the guys, attacking other boy bands, especially the Wanted

Recent dust-up: Last summer, Directioners went nuts when a British GQ cover featuring Harry Styles with the cover line, “He’s up all night to get lucky,” which they considered an attack on his purity. GQ and its staffers paid dearly.

Sample tweet: @devon_stratton: “@Harry_Styles I wish you and Kendall break up. It is not fair and I hate Kendall she sucks a whole lot.”

Recent dust-up: Barbz love a good feud, and Nicki’s had plenty of them, from her ongoing rivalry with Lil’ Kim to her “American Idol” tension with Mariah Carey. The Carey drama got a new burst of life last month when the two divas dropped new videos on the same day.

Sample tweet: @IamRossMathieu: “@MariahCarey YOU ONLY DO MUSIC FOR MONEY AND FAME SO F–K YOU”